/Engine/Source/Runtime/MessagingCommon/Public/MessageEndpointBuilder.h
WithHandler
template<typename HandlerType> [FMessageEndpointBuilder](API\Runtime\MessagingCommon\FMessageEndpointBuilder) & WithCatchall ( HandlerType * Handler, typename [TRawMessageCatchall](API\Runtime\MessagingCommon\TRawMessageCatchall)< HandlerType >::FuncType HandlerFunc )